The purpose of this research is to determine the effectiveness of two medications, tricyclic antidepressants (TCA) and opioids, compared to a placebo in the treatment of Post-Herpetic Neuralgia. The specific aims are to compare the effects of opioids and TCA against placebo on pain, altered skin sensitivity, and affective and cognitive function. In addition, the study will determine if the therapy with opioids or TCA affects cognitive function that may limit their usefulness in the treatment of PHN.